hey Physics Pholks

The starting formula is:

F = ma

F = force (Newtons)

m = what you're trying to find

a = acceleration (m/s^2 ... here you'll need to put the delta, or difference, in speeds over the time, makes the units work out)

P.S. That's Newton's 2nd Law, by the way.

Balance of forces in the initial state. The force applied on the block to move it will be equal to the sliding friction force (which is proportional to the weight of the block) opposing that.

5N applied = mass * friction coefficient

Increase the force, you have 1.5m/s/3s or .5m/s^2

12N applied - sliding friction force = mass * .5m/s^2

two equations to solve for mass and sliding coefficient.

This example gets you most of the way there: http://www.dynamicscience.com.au/tester/solutions/flight/velocity/force.htm

Look up the four kinematic equations for motion.

The average acceleration is  (3.5-2.0)/3      (v1-v0)/time  a = .5 m/s^2

F= ma

5= m(.5)

m = 10 kg

Been rethinking this.   The average acceration comes from the 12 newton force so that should be used instead of the 5 newton force.

12 = m*(.5)

mass = 24 kg.

That's what I got as well.

24kg is correct

12N = mass * ((3.5m/s - 2.0m/s)/3 sec)

Solve for mass

I can't wait.  I adored physics in HS.

Here's how I would tackle this problem...

Assumptions:

1) The force is applied horizontally

2) The block is on a flat surface with no incline

Scenario 1:

5N - Ff = 0 ...there is no acceleration, so the applied force equals the opposing force of friction

Ff = force of friction = coeff of friction * Normal Force ...assuming the block is on a flat surface with no incline, Normal Formal = Weight (which is m *g), so ... Ff = coeff of friction * m * g

Scenarion 2:

12 - Ff = ma

Now just solve the equations:

a = (3.5 - 2)/3 = 0.5 m/s^2

12-Ff = ma ... 12-5 = m * 0.5 ... m = 14g

You can then solve for the coeff of friction:

5 = coeff of friction * m * g ... coeff of friction = 5 / (14*9.81) = 0.0364

Yeah, you spend two hours doing AP Physics or Chemistry and then they forget to turn it in and get a zero. And then you have to explain to them that the reason they have a C average even though they have 100's on their 3 quizzes is that (100+100+100+0)/4 = 75. For example